Convert CONFIG_USE_BOOTCOMMAND et al to Kconfig

This converts the following to Kconfig:
   CONFIG_USE_BOOTCOMMAND
   CONFIG_BOOTCOMMAND
   CONFIG_RAMBOOTCOMMAND
   CONFIG_NFSBOOTCOMMAND

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/integratorap_cm920t_defconfig b/configs/integratorap_cm920t_defconfig
index e03db98..3ff47e1 100644
--- a/configs/integratorap_cm920t_defconfig
+++ b/configs/integratorap_cm920t_defconfig
@@ -9,6 +9,7 @@
 CONFIG_SYS_LOAD_ADDR=0x7fc0
 CONFIG_USE_BOOTARGS=y
 CONFIG_BOOTARGS="root=/dev/mtdblock0 console=ttyAM0 console=tty"
+CONFIG_USE_BOOTCOMMAND=y
 # CONFIG_DISPLAY_CPUINFO is not set
 # CONFIG_DISPLAY_BOARDINFO is not set
 CONFIG_MISC_INIT_R=y